1. Field of the Invention
This invention relates to a variable reluctance type angle detector comprising a rotor having such a shape that a gap permeance varies in a sine wave fashion with respect to an angle θ, the rotor being rotatable with respect to a stator in which an excitation wire and an output wire are wound around tooth members.
2. Description of the Related Art
As a conventional variable reluctance type angle detector, the one having a rotor provided rotatably inside a stator is known. The stator has a stator core provided with twelve tooth members, for example, projecting inward and disposed in a circle. An excitation wire and a two-phase output wire are wound around each of the tooth members of the stator core.
The excitation wire is wound around each of the tooth members in such a manner that a polarity is alternated successively along a circumferential direction. The excitation wire wound around each of the tooth members forms an excitation coil. The two-phase output wire is wound around the tooth members so as to obtain a SIN output and a COS output that are different in phase from each other by 90°. The two-phase output wire wound around each of the tooth members forms an output coil. The rotor has such an outer shape that a gap permeance between the rotor and the stator varies in a sine wave fashion with respect to an angle θ. When the rotor rotates, an excitation voltage supplied to the excitation wire is outputted from one of the output wires as a COS output voltage while being outputted from the other output wire as a SIN output voltage. Such variable reluctance type angle detector is disclosed in JP-A-H8-178611, for example.
Shown in FIGS. 5 and 6 is one example of the conventional winding structure. In the winding structure, an excitation wire 93 and an output wire 94 are wound around twelve tooth members 91 in the form of two layers. A stator core constituting each of the tooth members 91 is provided with an end insulator 92. The end insulator 92 provides an insulating coating on the tooth members 91. The excitation wire 93 is wound around the twelve tooth members 91 positively and negatively.
As the output wire 94, the one outputting a COS output voltage and the one outputting a SIN output voltage are used. The output wires 94 are wound around predetermined tooth members 91 to achieve a COS output and a SIN output depending on the number of the positive windings and the number of negative windings. Either one of the COS outputting or SIN outputting output wires 94 is wound around each of the predetermined tooth members 91. The type of the output wire 94 and the number of the positive windings or negative windings on the tooth member 91 are appropriately set, and these settings are omitted in FIG. 5. The excitation wire 93 is wound around each of the tooth members 91. The output wire 94 is wound from the outside of the excitation wire 93.
As shown in FIG. 6, the excitation wire 93 and the output wire 94 are wound around the tooth members 91 from outside the end insulator 92 as two layers. Though not shown in FIG. 6, each of the excitation wire 93 and the output wire 94 is coated with an enamel layer. The enamel layer prevents electrical short which is otherwise caused between the excitation wire 93 and the output wire 94.
As shown in FIGS. 7 and 8, projections 96 are provided on an outer periphery of the end insulator 92. Winding start portions and winding end portions of the excitation wire 93 and the output wire 94 wound around the tooth members 91 are tied to the projections 96. Crossovers of the excitation wire 93 or the output wire 94 for gaps between the adjacent tooth members 91 are also tied to the projections 96. In the winding start portions, the winding end portions, and the crossovers, the excitation wire 93 and the output wires 94 are brought into contact with each other and the excitation wire 93 is brought into contact with itself or the output wire 94 is brought into contact with itself.
In the above-described conventional variable reluctance type angle detector, insulation for the contact portions between the excitation wire 93 and the output wire 94, the contact portions of the excitation wire 93, and the contact portions of the output wires 94 are ensured by the enamel layers which are skin portions of the excitation wire 93 and the output wires 94. In general, along with an increase in contact portion between wires, a probability for occurrence of insufficient insulation is increased. As one of the causes for the insufficient insulation, stripping of the enamel layer is considered. Also, the enamel layer can be stripped off with time by vibration or the like during use. The incipient failure due to the insufficient insulation reduces a yield of product. The insufficient insulation with time deteriorates reliability of the product.